The favourite to be South Korea’s next president has come under fire for saying during a TV debate that he does not like homosexuality.
Moon Jae-in’s comments caused a LGBT rights group to crash one of his campaign events in protest.
The former human rights lawyer had enjoyed strong support among young, liberal voters, but surprised many on Tuesday when he said: “I do not like it” when asked if he opposed homosexuality.
Mr Moon, a practising Catholic, said he had “no intention” to legalise same-sex marriage.
He was responding to a question from a conservative presidential candidate who said gay soldiers were weakening the military.
Mr Moon added that no one should be discriminated against due to their sexual orientation, but it failed to calm the controversy.
Homosexuality is not a crime in South Korea but the country remains conservative and patriarchal.
Many gay and transgender people are stigmatised and a powerful Christian lobby has opposed bringing in anti-discrimination laws.
South Korea’s military has also been accused of hunting down and prosecuting gay servicemen.
A day after the remarks, protesters turned up with rainbow flags at Mr Moon’s campaign event in Seoul, shouting comments such as “Apologise for hate remark” and “Are you opposing my own existence?”
Thirteen people were detained and some dragged away, said campaign group Solidarity for LGBT Human Rights of Korea.
Some of Moon’s supporters defended his comments as matching the views of many in the country.
The country’s election, held on 9 May, was called after President Park Geun-Hye was removed from office in March over a corruption scandal.